Two Britons, one believed to be a NHS doctor, have been arrested in the first case of the Syrian civil war leading to the arrest of suspected terrorists in the UK.

The man and woman were held by Scotland Yard detectives as they flew into Heathrow from Egypt.

The couple are being questioned, it is believed, over suspected terrorist activities including the kidnapping of a British and a Dutch photographer who crossed into Syria from Turkey two months ago. John Cantlie and Jeroen Oerlemans described being captured at gunpoint by a group of foreign fighters including “British Pakistanis”.

The two journalists were freed by members of the Syrian resistance who stormed the jihadist camp. The leader of the kidnap gang, The Independent can reveal, was subsequently executed by another rebel faction. The body of Abu Mohammed al-Shami al-Absi was found at Samada near the Turkish border two weeks after he disappeared in August.

Freelance photographer Mr Cantlie, who was shot along with Mr Oerlemans when they tried to escape, maintained later that he was treated by a doctor who spoke with a south London accent and was using saline drips with NHS logos on them. The pair’s captors boasted of their alliance with al-Qa’ida and had threatened to kill them. Mr Cantlie was reported to be helping police to identify whether or not the detained suspect is the medic he had met.

The couple, both 26, were arrested by officers the Yard’s Counter-Terrorism Command after they arrived on an 8.30am flight from Cairo and taken to a central London police station “on suspicion of the commission, preparation or instigation of acts of terrorism”. Searches were later carried out at a number of properties in east London.

British security sources yesterday refused to comment on reports from Syria that the arrests at Heathrow followed information supplied by the more “secular” elements of the Syrian opposition who had been liaising with SIS (MI6) operatives based in Istanbul and the Turkish capital Ankara on a regular basis since last Autumn.

Al-Absi worked with the Islamist Jobhat al-Nusra Brigade which had openly proclaimed it’s links to al-Qa’ida and has carried out a number of suicide bombings. His followers have accused the Al-Farouq brigade his killing.

The group, which has publicly stated its opposition to al-Qa’ida’s involvement in the conflict, denies responsibility. But one of its officers, Amar Mohammed Abadullah, told The Independent: “We are fighting for a democracy where all our people, Muslims and Christians, have a part to play. Obviously we cannot work with those who want to impose their own [version of an] Islamist state and act against those who disagree with them.”

Speaking about yesterday’s arrests, Mr Oerlemans said about his captors: “There wasn’t any woman anywhere, so that surprised me. But that doesn’t mean it’s not one of the guys in the camp. They were all 20-somethings so it might just well be the kidnappers.”

There has been an intrinsic difference between the Britons who had travelled to join in Libya’s revolution against the regime of Muammar Gaddafi and those who had joined the jihad in Syria.

Hundreds from the Libyan diaspora in Britain fought in the uprising. The Britons in Syria are estimated by MI5 to be no more than a “few dozen” although the actual figure, in reality, is even lower. However, most of them are not originally from Syria but other countries.

Foreign Secretary William Hague said: “We’ve had reports of course of foreign fighters including British people going to Syria. That’s not something that we recommend and we do not want British people going and taking part in violent situations anywhere in the world.”